Electron multiplier



Jan. 21, 1964 w. P. F. RAFFAN 3,119,038

ELECTRON MULTIPLIER Filed May 23. 1960 2 Sheets-Sheet l PA /0P A I? T INVENTOR.

WILLIAM PATTERSON FORSYTH RAFFAN A TTORN E Y Jan. 21, 1964 w. P. F. RAFFAN 3,119,038

ELECTRON MULTIPLIER Filecl May 23,1960 2 Sheets-Sheet 2 INVENTOR. WILL/AM PA TERSO/V FORSYTH RAFFA/V A T TOR/V5 Y United States Patent Gil lice atlases Patented Jan. 21, 1984 3,119,638 ELEQTRQN MULTEPLIER Wiliiam Paterson Forsyth Ralian, Merton Park, London, England, assignor to Bush and Rani: Cintel Limited,

London, England, a British company File-d May 23, 196i Ser. No. 31,119 Claims priority, application Great Britain May 25, 1959 8 Claims. (Cl. 313103) This invention relates to an electron multiplier of relatively inexpensive construction.

A well known prior electron multiplier, offering considerabie advantages with respect to gain characteristics, includes a series of dynodes formed generally as or defining open prismatic boxes of approximately quadrantal cross-section having two flat and one curved side and two flat, quadrantal ends. Electrons enter such a dynode through a grid structure which constitutes one of the fiat sides and impinge upon the inner or concave surface of the curved side. The electrons are then withdrawn by the field of the next successive stage through the other flat side which is left open. The common practice heretofore has been to form such dynodes from a sheet of the same metal which is to be used as a basis for the secondary-emissive dynode surface. Since the metals used to form dynode surfaces are usually expensive and often diificult to form, this known construction is disadvantageous and expensive.

It is therefore an object of the present invention to provide a new and improved electron multiplier.

It is another object of the invention to provide an electron multiplier in which economies in material may be achieved.

According to one aspect of the present invention, there is provided an electron multiplier comprising at least one dynode in which the secondary-emissive surface is formed on a member which is secured to a base member of different material so as to be capable of removal without requiring the employment of tools. Preferably, the secondary-emissive electrode is of simple geometrical shape. It is very conveniently secured to the base member of the dynode by tabs formed on the latter which are bent or crimped over after the secondary-emissive electrode is in place. Alternatively, it may sometimes be desirable to form the base member such that recesses or channels are presented into which the secondary-emissive electrode will slip when flexed. The channels then retain the secondaryemissive electrode.

In accordance with another aspect of the invention, a dynode arrangement for an electron multiplier comprises a base member of a material relatively susceptible to forming. There is a secondary-emissive electrode, including a secondary-emissive surface, of a material relatively diificult to form and of generally cylindro-segmental shape. At least one holding device, relatively permanently connected to the base member but removably connected to the electrode, mechanically connects the electrode to the base member.

According to a still further aspect of the invention, the base member has at least a portion which is generally cylindro-segmental shaped with convex and concave surfaces.

The features of this invention which are believed to be new are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood, however, by reference to the following description in conjunction with the accompanying drawings, in which:

FIGURE 1 is a cross-sectional view of the general type of electron multiplier to which the present invention is applicable;

FIGURE 2 is a sectional view of a dynode constructed in accordance with one embodiment of the invention;

FIGURE 3 is another sectional view of a dynode con structed in accordance with another embodiment of the invention and,

FIG. 4 is a perspective view of the dynode of FIG- URE 3.

FIGURE 1 illustrates a section through four successive dynodes 3, 6, '7 and 8 of an electron multiplier. E-lec trons, whose general path is indicated by the broken construction lines 1, 2, enter the first quadrantal dynode 3 through a Wire mesh 4 covering one of the flat sides. The electrons impinge upon or strike the internal, sensitized secondary-emissive surface 5 of the cylindro-segmental shaped secondary-emissive electrode of the dynode. This results in the emission of secondary electrons which are drawn away by the field of the next dynode 6, which is of identical construction as dynode 5 but is established at a potential positive with respect to that of dynode 5. In like fashion, the electrons are multiplied in dynode 6 and attracted to the higher potential of dynode 7, causing additional electron multiplication. Finally, the electrons developed in dynode 7 are drawn to dynode '8 by its higher potential such that the electrons produced at the open side of dynode 8 are multiplied to a considerable extent with respect to those provided at the input of dynode 3.

The conventional construction of such dynodes involves forming the curved or cylindro-segmental shaped surface, as well as the flat ends, from metal stamped from flat sheet. After suitable bending and spot welding, the mesh is secured by welding to the edges of the sheet members to cover the entrance side of the dynode. After the various dynodes have been secured in their correct relative positions and enclosed in an evacuable envelope, the necessary sensitization of the secondary-emissive surfaces is effected. Where the material, of which the secondaryemissive surface is to be formed, is itself unsuitable for forming, a layer of the material may be evaporated upon a dynode formed of some other material. This process is complicated and costly and may have a deleterious effect upon the mechanical strength of the dynode structure.

A disadvantage of this general construction is that should it be desired to change the material used to form the secondary-emissive surface, it will often be necessary to alter the tools used for forming the separate pieces. Some materials which may very advantageously be employed to form the secondary-emissive surface of a dynode, such as for example magnesium-silver alloys, are brittle and therefore can only be formed with considerable difficulty into the comparatively complex shapes found in the dynode.

In accordance with the present invention, therefore, the main portion of the dynode structure is formed of a suitable, easily shaped metal, such as nickel or a deep drawing quality nonmagnetic stainless steel, and the. secondary-emissive surface is formed on a member removably or detachably secured to the main section. In the embodiment of the invention illustrated in FIGURE 2, a dynode comprises a quadrantal box having a curved or cylindro-segmental shaped base member 9, two quadrantal shaped flat ends, one of which is designated It), and one flat side covered by an open, conductive mesh 11. The remaining flat side is open. In accordance with the invention, a cylindro-segmental shaped electrode 12 of a material which is readily rendered highly secondary emissive is secured by small clips or holding devices 13 against the concave surface of base member 9. Since secondary-emissive electrode 12 is of simple geometrical form, it may be made of a material such as a magnesium-silver alloy which, though difficult to form, offers advantages in the production of a high and uniform coefiicient of secondary emission. A further advantage exhibited by the construction of FIGURE 2 is that the expensive secondary-emissive member may be recovered and reprocessed if it is found that the multiplier, when constructed. does not have the characteristics expected.

The dynode arrangement of FIGURE 2 therefore comprises a base member 9 of a material relatively susceptible to forming and having at least a portion which is generally cylindro-segmental shaped with convex and concave surfaces. Secondary-emissive electrode 12 is of a material relatively difiicult to form and is also of genorally cylindro-segmental shape. Each of clips 13 constitutes a holding device, relatively permanently connected to base member 9 but removably connected to electrode 12, for mechanically connecting electrode 12 to base member 9.

FIGURES 3 and 4 illustrate another embodiment of the invention in which a quadrantal boxlike dynode is formed by a fiat mesh side 11, quadrantal end plates 10, and a cylindro-segmental secondary-emissive electrode 14 held in channel or recess members 15 extending between the spaced-apart end plates. Once again the more complex members of the dynode may be formed of nickel or a deep drawing quality non-magnetic stainless steel while the secondary-emissive member 14 may be of magnesiumsilver alloy.

In FIGURES 3 and 4, each of end plates may be considered a base member of a material relatively susceptible to forming. Each of channel elements is relatively permanently connected to each base member 10 but removably connected to electrode 14. Electrode 14, of course, is initially positioned in the dynode structure by compressing or flexing it such that it springs into the recesses or channels provided by elements 15.

It will be seen that by employing the present invention the necessity for welding or substantially forming the metals used to provide the secondary-emissive surface is conveniently avoided.

While particular embodiments of the invention have been shown and described, modifications may be made, and it is intended in the appended claims to cover all such modifications as may fall within the true spirit and scope of the invention.

I claim:

1. A dynode arrangement for an electron multiplier comprising: a base member of a material relatively susceptible to forming; a secondary-emissive electrode of a secondary-emissive material relatively ditficult to form and of generally cylindro-segmental shape; and at least one holding device, relatively permanently connected to said base member but removably connected to said electrode, for mechanically connecting said electrode to said base member.

2. A dynode arrangement for an electron multiplier comprising: a base member of a material relatively susceptible to forming; a secondary-emissive electrode of a secondary-emissive material relatively difficult to form and of generally cylindro-segmental shape; and a pair of spaced-apart, parallel holding devices, relatively permanently connected to said base member but removably connected to said electrode, for mechanically connecting said electrode to said base member.

3. A dynode arrangement for an electron multiplier comprising: a base member of a material relatively susceptible to forming and having at least a portion which is generally cylindro-segmental shaped with convex and concave surfaces; a secondary-emissive electrode of a secondary-emissive material relatively difficult to form and also of generally cylindro-segmental shape; and at least one holding device, relatively permanently connected to said base member but removably connected to said electrode, for mechanically connecting said electrode to said base member adjacent its concave surface.

4. A dynode arrangement for an electron multiplier comprising: a pair of spaced-apart base members of a material relatively susceptible to forming; a secondaryemissive electrode of a secondary-emissive material relatively difficult to form and of generally cylindro-segmental shape; and at least one holding device, relatively permanently connected to each of said base members but removably connected to said electrode, for mechanically connecting said electrode to said base members.

5. A dynode arrangement for an electron multiplier comprising: a base member of a material relatively susceptible to forming and having at least a portion which is generally cylindro-segmental shaped with convex and concave surfaces; a secondary-emissive electrode of a secondary-emissive material relatively difiicult to form and also of generally cylindro-segmental shape and at least one holding device, mechanically connected to said base member, for removably connecting said electrode to said base member adjacent its concave surface.

6. A dynode arrangement for an electron multiplier comprising: a base member of a material relatively susceptible to forming and having at least a portion which is generally cylindrosegmental shaped with convex and concave surfaces; an electrode, also of generally cylindro-segmental shape having a convex surface and a secondary-emissive concave surface and of a secondaryemissive material relatively difficult to form and at least one holding device, mechanically connected to said base member, for removably connecting said electrode to said base member with the convex surface of said electrode being adjacent the concave surface of said base member.

7. A dynode arrangement for an electron multiplier comprising: a base member, of a material relatively susceptible of forming, having at least a portion which is generally cylindro-segmental shaped with convex and concave surfaces and also having a pair of tab portions; and a secondary-emissive electrode, including a secondaryemissive 'surface, of a material relatively difiicult to form and also of generally cylindro-segmental shape, said tab portions being crimped to hold said electrode adjacent the concave surface of said base member.

8. A dynode arrangement for an electron multiplier comprising: a pair of spaced-apart base members of a material relatively susceptible to forming; a pair of spacedapart parallel channel elements mechanically connected to said base members; and a secondary-emissive electrode, including a secondary-emissive surface, of a material relatively difiicult to form and of generally cylindro-segmental shape, said electrode removably held by said channel elements.

References Cited in the file of this patent UNITED STATES PATENTS 2,245,624 Teal June 17, 1941 

1. A DYNODE ARRANGEMENT FOR AN ELECTRON MULTIPLIER COMPRISING: A BASE MEMBER OF A MATERIAL RELATIVELY SUSCEPTIBLE TO FORMING; A SECONDARY-EMISSIVE ELECTRODE OF A SECONDARY-EMISSIVE MATERIAL RELATIVELY DIFFICULT TO FORM AND OF GENERALLY CYLINDRO-SEGMENTAL SHAPE; AND AT LEAST ONE HOLDING DEVICE, RELATIVELY PERMANENTLY CONNECTED TO SAID BASE MEMBER BUT REMOVABLY CONNECTED TO SAID ELEC- 